| wrote:

I noticed that that all the following posting assume
some form of fission nuclear power. I'll suggest
that fusion might be the 'ultimate' power source
for a grand interplanetary drive. Though it might
need a fission reactor for jump start power. The
ideal would be a deuterium/boron fusion reactor though
that needs much work. Then again aneutronic fusion
maybe too 'Star Trekie' to be practical anytime in
the next century or two.

Until then the best impulse available is from low thrust long running
electric ion drives that have been used on plenty of missions so far.

For such drives the limiting factor is the energy available to power the
drive continuously. Solar cells should be plenty in Earth orbit for
station keeping and orbit maintenance but interplanetary missions would
work far better with more power available. A nuclear reactor could
supply power for both the drive and the rest of the vehicle.

But how to get one safely aloft or enough infrastructure in place to be
able to build one from spaceborn raw materials ...